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//#include <iostream>
#include <vector>
#include <string.h>
#include <fstream>
using namespace std;
vector <int> primes;
ifstream cin ("ciur.in");
ofstream cout("ciur.out");
void check_primes(int n){
vector <int> pr(2000001);
primes.push_back(1);
for(int i = 2; i <= n/2; ++i){
if(pr[i] == 0){
for(int j = i+i; j <= n; j += i)
pr[j] = 1;
primes.push_back(i);
}
}
}
int main(){
int n;
cin >> n;
check_primes(n);
cout << primes.size();
return 0;
}